Fabrication of Compressed Hosiery and Measurement of its Pressure Characteristic Exerted on the Lower Limbs

Summary

This article reports fabrication, structure and pressure measurement of compressed hosiery by employing direct and indirect methods.

Abstract

This article reports the pressure characteristic measurement of compressed hosiery via direct and indirect methods. In the direct method, an interface sensor is used to measure the pressure value exerted on the lower limbs. In the indirect method, the necessary parameters mentioned by the cone and cylinder model are tested to calculate the pressure value. The necessary parameters involve course density, wales density, circumference, length, thickness, tension, and deformation of the compressed hosiery. Compared with the results of the direct method, the cone model in the indirect method is more suitable for calculating the pressure value because the cone model considers the change in radius of the lower limb from the knee to the ankle. Based on this measurement, the relationship among fabrication, structure, and pressure is further investigated in this study. We find that graduation is the main influence that can change the wales density. On the other hand, elastic motors directly affect the course density and the circumference of the stockings. Our reported work provides the fabrication-structure-pressure relationship and a design guide for gradually compressed hosiery.

Introduction

Compressed hosiery (CH) provides pressure on the lower limb. It can press the skin and further change the vein radius. Thus, the venous blood flow velocity is raised when the patient is dressed in compressed hosiery. CH and other compressed garments could improve venous circulation in the lower limbs^1,2,3,4. The therapeutic performance was dependent on the pressure characteristics of the CH⁵. It was widely believed that raw material and CH structure have a great influence on CH pressure characteristics. Elastane yarn in CH was primarily responsible for the pressure characteristics according to some published research⁶. For example, Chattopadhyay⁷ reported the pressure characteristics of knitted circular stretch fabrics by adjusting the feed tension of elastane yarn. In addition, Ozbayraktar⁸ also determined that the density of elastane yarn increased while the extensibility of CH decreased. Additionally, loop length⁹, knitted pattern⁹, and linear density of the yarns^7,10 also exhibited the effects on the pressure characteristics.

A numerical model was presented to inspect the generation mechanism of the pressure characteristics of the CH. Laplace’s Law was used for predicting the pressure values. Thomas¹¹ introduced Laplace’s Law into pressure prediction by combining pressure, tension, and body limb size. Similar work also was reported by Maklewska¹². To precisely predict the pressure values exerted by the fabric, they presented a semi-empirical equation that was composed of the fitted stress-strain equation and Laplace’s Law. Additionally, Young’s modulus was presented by Leung¹³ to describe elongation of the CH.

The above-mentioned numerical studies showed deviated experimental results due to ignorance of the CH thickness¹⁴. In addition, some researchers believed that the hypothetical cylinder involved in Laplace’s Law was inappropriate to describe the body limbs because the radius of the lower limbs from the thigh to the ankle is not constant but gradually decreases. By combining the thick cylinder theory and Laplace’s Law, Dale¹⁴ and Al Khaburi^15,16 respectively proposed numerical models to investigate the pressure exerted by the CH with multiple layers. Sikka¹⁷ presented a new cone model with a gradually decreased radius from the thigh to the ankle.

The pressure characteristics intrinsic to CH were difficult to quantitatively study because most of the experimental CHs in previous studies were usually purchased commercially. The influences such as pattern, yarn, raw material were uncontrollable. Therefore, in this study, the experimental CHs were controllably fabricated in house. Moreover, this study aims to provide two methods involving direct method and indirect method to measure the pressure characteristics. In the direct method, an interface sensor (Table of Materials) is placed between the skin and textiles to directly measure the pressure value. On the other hand, in the indirect method, the tension and some structure parameters of the CH sample dressing on the artificial lower limb are firstly measured. Then, the results are substituted into the cone model and the cylinder model to calculate the pressure value. The pressure values obtained as a result of the two methods are contrasted and analyzed to find a more appropriate model. The presented methods provide a guideline to the experimental measurement of pressure exerted by the compressed garment.

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Protocol

1. Fabrication of CH

1. Programming
   1. Open the STAT-Ds 615 MP stocking software and select Plain fabric to create a new sock construction.
   2. Select the following contents in order: Double welt 1 feed, Transfer without pattern, Plain medical leg from double welt 1 feed, Begin heel from plain medical leg, End of heel and plain medical foot, Begin toe from plain foot 1f, Plain toe with rosso and clip, Sock release without turning device, and End of sock. Press OK button to complete the sock design.
   3. Select 200 for the Needle and export the program file onto a USB flash disk.
   4. Switch to Quasar to change the fabrication parameters and click any blue button in the GRADUATION row to open a new window. For fabricating the CH with different structure, enter 500 in the Cylinder S and E columns and click OK to complete the setup.
   5. Click any one of blue buttons in the ELASTIC MOTORS row to open a new window and enter 800 in the WELT rows and the Cylinder S and E columns. In the Medical leg row, enter 800 in the S column and 650 in column E. Then enter 650 in the ANKLE row and the S and E column and click OK to complete the setup.
   6. Repeat steps 1.1.4 and 1.1.5. Respectively enter 350 and 650 when adjusting GRADUATION. Respectively enter 1000 and 1200 in the WELT row, and keep the ANKLE row as 650 when adjusting ELASTIC MOTORS.
      NOTE: The elastic motors could control the tension of the elastane yarn. Fabricated CH should ensure that the tightness gradually increased from knee to ankle. Here, the elastic motor number in the ANKLE is fixed (650), while the elastic motor number in the WELT is changed (800, 1000, 1200) to fabricate CH samples with different tightness. The graduation could control the loop size of the whole CH sample. Larger loops usually result in looser CH, while smaller loops always generate a tight CH sample. Thus, we respectively input 350, 500, and 650 as the graduation. Finally, program files with altered elastic motors and graduation are generated.
2. Knitting
   1. Prepare the ground yarn and elastane yarn on the CH fabrication machine.
   2. Turn on the machine, insert the USB flash disk, and select the program file obtained from step 1.1.3. The machine will automatically fabricates the CH sample. Alphabetically number these samples from A to I.
      NOTE: Table 1 displays the fabrication parameters of these CH samples.

2. Direct measurement

NOTE: All of the CH samples should be conditioned for 24 h in standard atmospheric environment (23 °C, 65% relative humidity [RH]) prior to measurement. The CH samples are dressed on the artificial lower limb to test the pressure value. All measurements should be performed three times to calculate the average value and decrease the error.

1. Mark the lines on the CH sample.
   1. Place a sample onto an artificial lower limb.
   2. Mark six, evenly spaced, circle lines on the compressed hosiery sample dressings from the knee to the ankle. Number these lines as line 6, 5, 4.... These lines divide the CH sample into five parts, as shown in Figure 1a.
2. Pressure measurement
   1. To perform a pressure measurement, place the interface pressure sensors under part 1 of the compressed hosiery sample in the anterior, posterior, medial, and lateral directions.
   2. In the measurement software, select the appropriate serial port COM and set the minimum threshold value as 0.
   3. Click Start Measurement. Real-time channel 1~4 will display the pressure data
   4. When the pressure is stable, click Stop Measurement. The software will automatically export the pressure data.
   5. Place the interface press sensors under other parts of CH sample and repeat steps 2.2.1−2.2.4.
3. After pressure measurement of the whole CH sample, remove the CH sample and then dress another CH sample on the artificial lower limb to prepare for the next measurement.

3. Indirect measurement

NOTE: The experiments here measure the necessary parameters of the cone and cylinder model. These parameters contain the deformation and structure parameters of the dressing and undressed CH samples, thickness, tension. All the CH samples should be conditioned for 24 h in standard atmospheric environment (23 °C, 65% RH) prior to measurement. All measurements should be performed three times to calculate the average value and decrease the error.

1. Structure parameter measurement of CH samples
   1. Place a CH sample on the artificial lower limb.
   2. Use a measuring tape to measure the total length (L) of the sample.
   3. Use a pick glass to measure the course density and the Wales density of each divided part.
   4. Measure the circumference (c) of each circle line with measuring tape. Then, calculate the circumference (w) of each divided part of the CH sample by averaging the circumferences (c) of the neighboring circle lines.
   5. When all of the structure parameter measurements have been acquired, remove the sample from the limb. And then dress another sample on the artificial lower limb to prepare for next measurement.
   6. Measure the circumference (c’) of each circle line of an undressed CH sample. Then, calculate the circumference (w’) of each divided part of CH sample by averaging the circumferences of the neighboring circle lines.
   7. Measure the course density and the wales density of the same divided part of the undressed CH sample.
2. Thickness measurement
   1. Smooth a compressed hosiery sample onto the steel round table of the thickness gauge.
   2. Turn on the thickness gauge to let another steel round slowly fall down to press onto the sample piece. The screen will display the thickness data (t).
   3. Move the sample and repeat steps 3.2.1 and 3.2.2 to test the thickness of other parts.
3. Tensile experiment
   1. Cut all the CH samples along the marked circle lines.
   2. Clamp one piece of sample into the tensile testing instrument.
   3. Open the software for tensile experiment, input 5 N as the initial tension, 60 mm/,min as the tensile speed, and 200 mm as the initial tensile length. Keep the default setup for the other fields.
   4. When all of the measurement parameters have been set, click START to run tensile experiment automatically. The computer will export real-time stress and strain on the screen. The tensile experiment will automatically stop when the CH piece is broken.
   5. Then replace the broken piece of sample with a new sample piece for the next round of testing and repeat steps 3.3.3−3.3.4.

4. Theoretical calculation

NOTE: The cylinder model and cone model are employed in the indirect measurement to calculate the exerted pressure. Each CH sample is separated into five parts from the knee to the ankle. In the cylinder model, human limbs are described as a cylinder with a constant radius while the radius of the limb is variable in the cone model. The schematic diagrams are illustrated in Figure 1b and Figure 1c. All calculation steps are performed in Matlab 2018a and the calculation program can be found in the Supplemental Coding File.

1. Cylinder model
   1. According to the measured results obtained from step 3.1.3−3.1.5, calculate the circumference difference (D) between the dressed CH and the undressed CH using the following equation:
      
      where i is the number of CH piece that is separated by marked circle lines. It is numbered according to the circle line number.
   2. Fit the stress-strain curve obtained in step 3.3.4 using an appropriate linear equation. The slope of the linear equation is the tensile modulus E.
   3. Calculate the tension in the dressing CH (T) by employing the equation:
      
      NOTE: Supplemental Table 1 displays the obtained original tensile modulus E and tension T.
   4. Based on the cylinder model and the thin wall assumption¹⁵, express the exerted pressure of CH piece i as:
      
      where r is the radius of divided part and equals to , t is the thickness of CH sample, and T is the tension calculated from step 4.1.3.
   5. Calculate all the exerted pressure of CH pieces following steps 4.1.1−4.1.4.
2. Cone model
   1. Calculate the exerted pressure of the CH piece i by the following equation¹⁴:
      
      where r_c is the radius of circle line and equals to , T is the tension calculated from step 4.1.3, l is the length of each divided piece and can be calculated by l = L/5 (herein, L is measured following step 3.1.2).

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Results

Course density gradually increases from the knee to the ankle in Figure 2a. This is explained by the influence of the elastic motor. From the knee to the ankle, the increased elastic motor gradually generates increasing tension from part 5 to part 1 in the CH fabrication process. Thus, the CH sample is gradually frapped and the loop number per cm is increased in the course direction. The experimental lines in Figure 2b can be divided into three groups: ABC, DEF,...

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Discussion

In this study, we provide two methods to measure the exerted pressure of CH samples and these methods can be used to measure the exerted pressure of other garment dressing on the skin. In the direct method, the CH sample is dressed on the artificial lower limb and the interface sensor is placed under the CH sample. The pressure value can be displayed on the screen using data collection software. To compare with the direct method, we also supply an indirect method. Two theories involving the cylinder model and the cone mo...

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Materials

Name	Company	Catalog Number	Comments
Artificial lower limb	Dayuan, Laizhou Electron Instrument Co., Ltd.	YG065C	Used for measuring the strength of stockings. The employing test standard is ISO 13934-1-2013, metioned this in section 3.3
CH fabrication machine	Hongda, Co., Ltd.	YG14N	Used for measuring the thickness of stockings, the test standard is ISO 5084:1996, metioned this in section 3.2
Elastane yarn	MathWorks, Co., Ltd.	2018a	Used for calculating the pressure, mentioned this in section 4.
FlexiForce interface pressure sensors	Qile, Co., Ltd.	Y115B	It is composed of magnifying glass with a fixed ruler. Used for counting the loops number per cm in the fabricated CH, metioned this in the sction 3.1.3 and 3.1.7.
FlexiForce measurement software	Santoni, Co., Ltd.	GOAL 615MP	Used for fabricating stockings, metioned this in section 1.2
Ground yarn	Santoni, Co., Ltd.		It is a kind of coverd yarn which is composed of 80% rubber and 20% viscose, metioned this in section 1.2.1
Matlab software	Santoni, Co., Ltd.		It is a kind of coverd yarn which is composed of 30% polyamide and 70% cotton, metioned this in section 1.2.1
Mechanical testing instrument and software	Santoni, Co., Ltd.	GOAL 615MP	Used for programing the fabrication parameters, metioned this in section.1.1
Pick glass	Shenmei, Inc.	F002	A standard artificial femal with 160 cm height. The size was consited with Chinese Standard GB 10000-1988. The artificial femal was made by glass-reinforced plywood and covered by fabric. Mentioned this in section 2.1.
STAT-Ds 615 MP stocking software	Tekscan, Inc.	A201	Used for measuring the pressure on the skin, metioned this in section 2.2.1
Thickness gauge	Weike, Co., Ltd.	1lbs	Used for recording the pressure, metioned this in section 2.2.2-2.2.4.